Add css class choice in 'Add Media' modal

Hi all,

There has been legacy posts about this from a few years back that I have found but nothing seems to work in current WordPress.

What i need to achieve is some code that put in either a drop down of ‘classes’ to choose from or a text box in order to type in the class name when inserting an image into a page/post.

Found a few people who had achieved this a few years back with code in their functions.php file but nothing is working for me so I am guessing with updates it has been re-jigged and now doesn’t work.

Any one got a solution to this would be amazing!
(don’t know why things like this aren’t already included..)

Cheers!